In media handling assemblies, particularly in printing systems, strong, consistent, and reliable tacking of the substrate media, such as a sheet of paper, to the media transport (hold-down transport in the print zone or image transfer zone, in this case a belt) is necessary. FIG. 1 depicts an exemplary production printing system that could make use of the semi-conductive media transport. Media is transported from a storage tray onto the belt using a traditional nip based registration transport with nip releases. As soon as the leading edge of the media is acquired by the belt, the registration nips are released. The substrate media is generally conveyed within the system in a process direction.
In order to ensure good print quality in direct to paper (DTP) ink jet printing systems, the media must be held extremely flat in the print zone. The belt itself is held flat against a platen. Further, once accurate registration of the substrate media is achieved, the media cannot be allowed to move out of registration as it is delivered to the print zone. Contemporary systems transfer media by means of laterally spaced apart drive rollers in registration nip assemblies. The rollers do not hold the media flat, and can subject the media to misalignment. Media acquisition by the belt can be by electrostatic tacking. The electrostatic tacking has the advantages of holding the media flat, and eliminating registration shift. In addition, a vacuum on the platen may be used to ensure flatness. A problem arises in that friction induced tribo-electric charges between the belt and the platen (and elsewhere) generate undesirable electrostatic fields in the ink ejection area which may adversely affect print quality. The use of a conductive belt will circumvent this but this can make it difficult to achieve desirable low, controlled fields between the media and a print head over a wide range of media properties.
One problem sometimes encountered in electrostatic tacking is charge migration and subsequent loss of tacking force between the media and the belt. This problem can be minimized by utilizing an insulating belt as a media transport. To avoid tribo-induced electric fields, a belt with sufficient conductivity, that is, a semi-conductive belt is desirable.
Accordingly, it would be desirable to provide an apparatus capable of holding the media flat by electrostatic tacking, and of ensuring tacking performance, while reducing tribo-induced electric fields, thereby avoiding the problems associated with the prior art.